e. The eye and ear objection you have not so
satisfactorily answered, and to me the difficulty exists of how _three
times over_ an organ of sight was developed with the apparatus even
approximately identical. Why should not, in one case out of the three,
the heat rays or the chemical rays have been utilised for the same
purpose, in which case no translucent media would have been required,
and yet vision might have been just as perfect? The fact that the eyes
of insects and molluscs are transparent to us shows that the very same
limited portion of the rays of the spectrum is utilised for vision by
them as by us.

The chances seem to me immense against that having occurred through
"fortuitous variation," as Mivart puts it.

I see still further difficulties on this point but cannot go into them
now. Many thanks for your kind invitation. I will try and call some day,
but I am now very busy trying to make my house habitable by Lady Day,
when I _must_ be in it.--Believe me yours very faithfully,

ALFRED R. WALLACE.

* * * * *

_Down, Beckenham, Kent. July 27, 1872._

My dear Wallace,--I have just read with infinite satisfaction your
crushing article in _Nature_.[90] I have been the more glad to see it, as
I have not seen the book itself: I did not order it, as I felt sure
from Dr. B.'s former book that he could write nothing of value. But
assuredly I did not suppose that anyone would have written such a mass
of inaccuracies and rubbish. How rich is everything which he says and
quotes from Herbert Spencer!

By the way, I suppose that you read H. Spencer's answer to Martineau: it
struck me as quite wonderfully good, and I felt even more strongly
inclined than before to bow in reverence before him. Nothing has amused
me more in your review than Dr. B.'s extraordinary presumption in
deciding that such men as Lyell, Owen, H. Spencer, Mivart, Gaudry, etc.
etc., are all wrong. I daresay it would be very delightful to feel such
overwhelming confidence in oneself.

I have had a poor time of it of late, rarely having an hour of comfort,
except when asleep or immersed in work; and then when that is over I
feel dead with fatigue. I am now correcting my little book on
Expression; but it will not be published till November, when of course a
copy will be sent to you. I shall now try whether I can occupy myself
without writing anything more on so difficult a subject as Evolution.

I hope you are now